One type of oil and gas well drilling involves drilling with a casing string rather than drill pipe. Typically, the operator rotates the casing string to cause rotation of a drill bit at the bottom of the casing string. In one technique, the drill bit is part of a retrievable bottom hole assembly. The bottom hole assembly has a drill lock assembly on its upper end that releasably locks the bottom hole assembly to the casing string to transmit torque as well as weight. The drill bit and an underreamer are mounted to the lower end of the bottom hole assembly. The bottom hole assembly may be retrieved and re-run for repair. The bottom hole assembly is also retrieved at the total depth for cementing the casing string in the well.
A profile sub with an internal annular recess and a set of splines is connected into the casing string near or at the bottom. The drill lock assembly has dogs that will engage the annular recess to transmit axial force. The drill lock assembly also has torque transfer members that move out into engagement with the splines to transfer torque.
A variety of drill lock assemblies are known. All require mechanisms to move the axial load and torque transfer members between locked and unlocked positions. While some of these assemblies are successful, reducing the complexity is desirable.